FBM201 output signal module

An enamel-coated steel cabinet has a radiant heat value of 5.5 W/m2 and °C. Installing a fan inside the cabinet will even out the temperature, while moving air provides considerably better cooling than still air. A suitable fan is a 120 x 120 mm axial fan, available in 24 V DC, 115 and 230 V AC. Install the fan so that it sits in the cooler area and will blow cold air against the operator panel. If the fan is mounted at the top and sucks air upwards, the fan’s ambient temperature will be higher = shorter lifespan. A good fan with a ball-bearing mounting has an expected lifespan of at least 40,000 hours (not a guaranteed lifespan) at 40 °C. This corresponds to at least 4 years of continuous use. If a thermostat is installed, the fan only needs to come on when needed

Large graphic terminals draw 

only one fifth of the current when the background lighting is off. The loss effect drops from e.g. 25 W to only 5 W. The operator panel’s loss effect = supply voltage x current. Virtually no power goes to external users and no loss effects due to inputs.

If you use a power supply that meets safety standards and only feeds the operator panel, there is no problem. 2. However, if you have a 24 V unit that also feeds other units, there is reason to be cautious. The operator panel does not have insulation that meets safety requirements in the event of a potential short circuit between 230 V AC and 24 V DC. It is assumed that the 24 V feed is secure, for example, SELV according to EN 60950 (protection against electric shock) and UL 950.

Here is an example that explains

 why a secure 24 V DC feed can be ruined by mixing 24 V relay contacts with 230 V AC relay contacts in a smaller controller. Check that the “clearances and creepage distances between 24 V DC and 230 V AC fulfill EN 60950 or UL 950”. If not, input a separate 24 V unit into the operator panel If there is a substantial distance between the relay contacts for 24 V DC and 230 V AC, it is OK to use the same 24 V devices for all feeds. 4. Connect 0 V on the 24 V feed to the ground. This offers three advantages: – Safety is increased. The 24 V feed will not be live in the event of a faulty connection or short circuit between 0 V (24 V) and 230 V phase. – Transients on the 24 V feed are connected to the ground. – No risk that the 24 V feed is at a high level in relationship to the ground. This is not unusual since there is high static electricity.